Steve is correct. The beam forms a cone so the balls at the edge of the screen are being viewed at an angle. This is very apparent when viewing vias. You cannot detect the density of the sidewall platings of the center via, but as you move toward the edge of the display area the side walls become more apparent. In reality the physical magnification due to the proximity of the sample to the tube varys slightly from the center to the edge. This means the locations of the balls and the diameters may be off slightly. Normally this is not too much of an issue since the variation is usually within the cutoff limits of the acceptance criteria. I never measure via diameter (for example) unless the via is centered in the crosshairs of the system. BGA measurements can be done across the display, and I'm sure most x-ray systems have compensated for the difference in physical magnification when they calculate the ball diameters based on edge density. Mark Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave | Westminster, CO 80234 USA | |email: [log in to unmask] | -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of stephengregory5849 Sent: Friday, January 22, 2010 7:23 PM To: [log in to unmask] Subject: Re: [TN] X-Ray Inspection You will have a "Fish-eye" effect with a lot of x-ray machines. Meaning that when you are viewing the whole image, the image of the balls in the center of the screen will appear to be a different diameter than the balls at the edges of the screen. You should only concentrate on what you see at the center of the screen, and manipulate and move the BGA around so that you can see all the balls in the center of the screen. Steve ----- Original Message ----- From: "Paul Edwards" <[log in to unmask]> To: <[log in to unmask]> Sent: Friday, January 22, 2010 8:59 PM Subject: Re: [TN] X-Ray Inspection Are you x-raying a BGA with a metal lid? Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ashok Dhawan Sent: Friday, January 22, 2010 11:22 AM To: [log in to unmask] Subject: Re: [TN] X-Ray Inspection Bob We are currently doing XRAY Inspection of BGAs. The XRAY TestEngineer noticed that solder ball size on outer rows is different from the ball size on inner core areas. "We are still seeing a bi-modal data distribution of ball volume between the middle and periphery balls? Is that normal for BGAs. " I would appreciate your expert comments as there is not much XRAY related information on web. Regards Ashok Dhawan Manuf. 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